I'm going to start running this is the next few months and I plan on making her not a child eating monster but instead a person that started netural but has gone a bit more chaotic evil in the last few thousand years. I like how in her stories she is annoyed at people bugging her especially if they want some of her magic.
My Black rider will paint her as saving Irrisen from a second world wound by creating the permanent winter (our table is a little loose with the world building). Irrisen is somehow connected to her homeland is why she cares. She replaces her daughters every 100 years because the first few kept getting so evil and currupt by that time that she was afraid they might loose control.
I don't think I need the geas and the rider has to give the PCs his blood in order for them to enter the hut and make the reconizable as allies to a few NPCs. It also gives his last bit of power to help them get to the hut. I do want to make sure they know that she beguilingly owes them a favor if they release her. In book 6 when they can start talking to her more and more as they remove layers of the doll, I want her to be very smart (but a bit forgetful), bitter, angry, and a little funny and charming.
I'm looking for more fairy tale flavor and may add the harrowing to book 4. I've already run 'murders mark' as a prequel and had the fortune teller give a few clues going all the way to book 5.